When counting Sefirat HaOmer, some people say La'Omer and some
say B'Omer. Which is right? Doesn't the fact that EVERYBODY says
"Lag B'Omer" prove that "B'Omer" is correct
and not "La'Omer?"

Dear Wendy,

Rabbi Nachman Bulman, shlita, explains that "everyone"
calls the day "Lag B'Omer" because the main proponents
of saying "B'Omer" are Rabbi Yitzchak Luria --
the Arizal -- and the Sephardi Kabbalists. Celebrating
Lag B'Omer with bonfires, music and dancing is largely rooted
in their kabbalistic teachings and traditions.

Most poskim say that "La'Omer" is correct. However,
both ways are valid, so there is no reason to change one's custom.
In fact, even if you say "today is day such and such"
-- omitting any reference to the "Omer" -- you fulfill
the mitzva.

By the way, not everyone calls it "Lag B'Omer."
The Shulchan Aruch refers to it as "Lag La'Omer."

Which reminds me of the two Jews who argued during their entire
plane ride regarding the correct pronunciation of Hawaii.

Upon landing in Honalulu, they asked the first native on the island
"Is it pronounced Hawaii or Havaii?"
"Havaii," he replied.
"Thank you," they said.
"You're velcome," said the native.